A forage harvester combines the functions of gathering, conveying, comminuting and transferring to transport vehicles harvested material such as corn, grass, cereal crops and plantation wood. The harvester is built on a frame, which is supported by a chassis. The self-propelled forage harvester is driven by a high power motor. The forage harvester is operated from a driver's cabin. The harvested material is gathered by means of a crop receiving device and fed to units for comminuting and conveying via intake units, wherein it is accelerated via an accelerator drum with a high rotational frequency and conveyed at high speed via a discharge tower into a discharge chute. The material flows along the upper inner wall of the discharge chute. A deflection of the material flow takes place according to the parabolic curvature of the upper inner wall of the discharge chute. The harvested material leaves the forage harvester via the discharge chute and a tiltable guide plate, which is articulated at its end, to a transport vehicle.
In order to direct the material flow to the transport vehicle, the discharge chute can be tilted by a (double acting) hydraulic cylinder around an axis of rotation on the discharge tower. At the same time, the discharge chute is rotatable about the vertical axis via a hydraulic motor and a gear wheel. During normal operation of the forage harvester, the discharge chute is raised to a working height and the material flow is thrown onto the trailer of a vehicle traveling alongside.
Measuring the crop mass flow is a prerequisite for the crop measurement, precision farming, mass-related billing for harvesting services, control and regulation of machine parameters such as maintaining a fuel-saving engine operating point as well as throughput-dependent regulation of the driving speed and throughput-proportional addition of additives, e.g., silage auxiliaries or preservatives.
A variety of solutions are described in patent documents and literature for determining the crop mass flow on forage harvesters. Different quantities are recorded by means of different physical principles which are related to the throughput of the crop.
A solution for determining the crop mass flow is based on the detection of throughput-proportional torques of conveying and/or comminuting units, e.g., by hydraulic pressure measurement on the hydraulic drive of infeed units (DE 10154874 A1) or hydraulic pressure measurement on the drive of the intake elements (WO 2003/039239A1).
To measure the crop mass flow, the measurement of the throughput-proportional distance between two pre-press rollers arranged in the conveying path of the crop flow is also combined with a force measurement in the region of the maximum limit position as well as a light barrier for detecting a low throughput (U.S. Pat. No. 6,401,549 B1).
The crop mass flow is also derived from the detection of the force effect upon impact and deflection of the crop flow onto an impact plate arranged in the discharge chute (US 2006/0046802 A1, U.S. Pat. No. 6,014,903, U.S. Pat. No. 5,736,652) or on a guide plate at the end of the discharge chute (Schmittmann, Osman, Kromer “Durchsatzmessung mit Feldhäcksler”, Landtechnik April 2000 p. 286-287).
Further work suggests a volumetric flow measurement of the crop, e.g., by measuring the crop flow cross-section in the discharge chute by means of laser scanners and the flow rate by means of Doppler radar (Schmittmann, Osman, Kromer “Durchsatzmessung mit Feldschäckslern”, Landtechnik April 2000 p. 286-287).
The mass flow-proportional deflection of conveying units such as press rollers (U.S. Pat. No. 5,795,221) is used for measuring the crop quantity on the forage harvester.
In the case of harvesting grass laid in a swath, the throughput is also derived from the dimensions of the grass swath before the receiving unit during grass cutting.
From the patent literature, further solutions are known for deriving the crop mass flow from vibro-acoustic machine parameters (SU 1396992, U.S. Pat. No. 6,874,304, U.S. Pat. No. 7,415,365).
The determination of the crop mass flow from the deflection of a sheet metal covering of a chopping unit by means of a laser interferometer (EP 1652421 A1) was also proposed.
Furthermore, a solution for the derivation of the crop mass flow is known by means of the air pressure difference between two measuring planes in the discharge chute (DE 4041995 A1) with a measuring plane close to the chopper drum and one at the end of the conically narrowing chute.
Capacitive measuring methods determine the crop mass flow using a measuring capacitor (DE4105857 C2).
The microwave attenuation, phase shifting and the measurement at several frequencies are to be used in DE 19648126 A1 for measuring parameters such as “material throughput, moisture, density, mass, etc.”.
Radiometric methods, e.g., attenuation by the flow of transmitted gamma, beta or x-ray radiation, have been proposed in WO 1985/000087 A1 but are not used in current practice.
Another possibility known from the literature is the weighing of the container which receives the crop material on a transport vehicle (ASAE Paper 021165, Won Suk Lee, Thomas F. Burks, John K. Schueller: Silage Yield Monitoring System).
In practice, systems with distance measurement on conveyor elements and the measurement of the material flow velocity are used. The systems require frequent calibration due to variable conditions. The function is restricted at low and high crop mass flows. At low crop mass flows, no or only a small deflection of the conveying elements occurs. At high mass flows, end positions of the conveying elements are reached, which prevent the measurement.
The abovementioned conventional systems presuppose a crop mass flow distributed evenly over the width of the conveying elements, which is often not the case.
The properties of the crop (dimensions of the crushed parts, their density, elasticity and compressibility, dry mass content) influence the achievable measuring accuracy.
The present state of the art for crop material measurement on forage harvesters also requires very frequent calibration by reference-weighing and has deficits at low and high crop mass flows and often requires a plurality of sensors. Furthermore, known systems have low social acceptance for radiometric methods and require complex equipment in vehicle-based weighing systems.
The present state of the art usually has indirect solution approaches for the derivation of the crop mass flow.